Queen Elizabeth II, 96, passed away on Thursday 8 September, with her family by her side in Balmoral.
In an official statement by the Palace, they said: "The Queen died peacefully at Balmoral this afternoon. The King and the Queen Consort will remain at Balmoral this evening and will return to London tomorrow."
The longest serving monarch's portrait adorns coins, notes and stamps, along with initials across government signage and post boxes across the country.
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So, what happens now?
The 4.5bn sterling banknotes in circulation with the Queen's face on will be replaced with the face of King Charles III.
It's not going to be a quick and easy process and is likely to take at least two years, according to The Guardian. Rather than current money being handed in and swapped out, it will be a gradual phase, with some Queen Elizabeth II coins being in circulation for many years to come.
Once Charles III new portrait is commissioned, millions of pounds of new currency will be printed and distributed by the Royal Mint.
The Queen's portrait branches beyond Britain, too, with her face on the currency of 35 countries, according to Guinness World Records. This includes Canada, New Zealand and coins and notes issued by the Eastern Caribbean central bank.
The official website of the Royal Household, Royal.uk, explained that the monarchs face the opposite direction to their immediate predecessor. This means that Charles III portrait is likely to face the left.
Stamps will also follow a similar process, with new stamps featuring Charles gradually coming into circulation.
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